Magnetorheological elastomers (MREs) are being used more and more for the development of isolators and absorbers to attenuate vibrations. In this study, four innovative multilayer MRE isolators with negative changing stiffness characteristics are prototyped for horizontal vibration reduction of a seat. For each MRE isolator, a magnetic system consisting of two permanent magnets and an electromagnetic coil was designed to realise negative changing stiffness. This performance of the MRE isolators was verified by the experimental results which indicate that the MRE isolators exhibit a controllable negative changing stiffness characteristic; and this was further verified by the measured natural frequency shift of the MRE isolators. An experimental platform was also developed to test the vibration suppression of the MRE isolators for a real truck seat suspension. The test results demonstrate that the ride comfort of the MRE isolator based seat suspension is significantly better than passive seat suspension.